Chemical modification studies of the active centre of Candida albicans chitinase and its inhibition by allosamidin.

Abstract

Allosamidin, a glycoside antibiotic, is shown to be a strong, competitive inhibitor of semi-purified chitinase from yeast cells of Candida albicans. The inhibitory potency of allosamidin was pH-dependent, with IC50 values of 280 nM at pH 5.0 and 21 nM at pH 7.5. At higher, micromolar, concentrations, allosamidin inactivated this chitinase in a time- and concentration-dependent manner. Kinetic studies of this inactivation provided evidence for the formation of a reversible complex between allosamidin and chitinase, characterized by Kinact = 5 microM, followed by irreversible modification of the enzyme with velocity constant k2 = 4.6 x 10(-3) s-1. Chemical modification studies with the use of group-specific reagents suggested the presence of Glu/Asp carboxyl group(s) at or near the active site, that were important for enzyme activity. The carboxyl-specific reagent, 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide, inactivated the chitinase in a single step process, with apparent second-order rate constant of 0.014 M-1 s-1.